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Roger Federer: "I fell into a negative spiral"

Roger Federer lost to Rafael Nadal in the quarterfinals at Indian Wells this season. (FREDERIC J. BROWN/AFP/Getty Images)

Roger Federer admits that he pushed his body too hard earlier this season, which may have contributed to his lackluster results.

Federer, who is competing at the Swiss Indoors this week, says he shouldn't have played after injuring his back in Indian Wells in March, and that he pushed his body too far during the German Tennis Championships and Swiss Open (two last-minute additions to his schedule) in July, AFP reports.

"I played matches that I should never have played," said Federer.

"I should have left in Indian Wells (last March, with back pain) before the quarter-finals against (Rafael Nadal). This summer, I should not have tried to play on clay in Hamburg and in Gstaad.

"But things always look better in hindsight. I wasn't able to train as I wanted during my seven-week break following Indian Wells. I fell into a negative spiral."

Federer has two more tournaments to solidify his spot at the ATP World Tour Finals in London. Two years ago, he won his last three starts -- the Swiss Indoors, Paris Masters and ATP World Tour Finals -- to set up a triumphant 2012 season in which he won Wimbledon and reclaimed the No. 1 ranking. Now ranked No. 7, Federer was realistic when asked about his chances to repeat the feat this season.

"I don't know if my level of play is strong enough to do it now," he said. "That would be a bit bizarre for me if I start saying that I'm going to win the last 15 matches of the season."

In the mix to qualify for the World Tour Finals is Federer's friend and countryman Stanislas Wawrinka, who is also playing in Basel. Wawrinka leads Federer by five points for the third-to-last spot in the eight-player field.

"I will be happy if [Wawrinka] qualifies," Federer said. "If that meant I will miss it, I honestly won't care. That means he was the better player for the year."